THE OTAIO

Hokitika Guardian, 8 November 1930, Page 6

THE OTAIO

EXPERT COMMENT. NEW FEATURES. LONDON, September 16Syren and Shipping devotes some space to a description of the Otaio, the new vessel for the New Zealand Shipping Company, which lias been launched at Barrow-in-Furness. The vessel, a large and last cargo liner, possesses some novel arrangements tor auxiliaiy drive.

According to this well-known shipping paper, these arrangements are novel, in as much as, while they are essentially electric in character, a greater and perhaps more economic use of exhaust gases from the two main engines has been made than hitherto, and the layout promises, if successful, to prove a rival to stereotyped methods of auxiliary powering on board ship. The Otaio’s service speed is to be 151 knots. Exhaust gas from the two main engines is passed through two Clarkson thimble tube silencer boilers with oil firing for port use. These boilers have a total output of 60001 b of steam at 1001 b per square inch working pressure. The steam generated by the heat of the exhaust gases passes to a steam engine-driven electric generator set of 160 kw. output, which supplies power for the operation of many of the principal auxiliaries while the ship is at sea. This, however, is not all in this very unusual arrangement, for the steam passes out of the last steam stage of the generator engine at 51b per square inch pressure, and is then used when necessary for accommodation heating purposes. It is also used for an evaporator set, and in this it makes 20 tons of fresh water per 24 hours. Alternatively, of course, in a ship of this arrangement with two-cycle engines it could be used to operate a (steam) turbo-blower for scavenger purposes, or even in a four-cycle installation in more or less stereotyped fashion for driving a supercharge blower. This arrangement (continues Syren and Shipping) is one which shows very great foresight coupled with a thorough appreciation of the technique of economic power generation in a fast modern motor liner. As has been suggested already, it is unlikely that such an arrangement could ever seriously challenge the present position of the Diesel engine-driven generator, although it must inevitably have a modifying effect upon it, particularly for tanker work, in which there is considerable scope for the adoption of a good typo of waste heat oil-fired exhaust gas boiler in place of the large and heavy Scotch boilers at present used. The

main reason for their retention seems to be the very positive nature of' their action and the need for such large quantities of steam, particularly in the dirty oil trades. For cargo ships, and in particular for tramps, the uses of this technique is well worthy of consideration. Much depends, of course upon the type of main Diesel engine selected, but it is interesting to note that there are on the market both fourcycle and two-cycle units capable of giving perfectly satisfactory “exhaust gas” service.